I got this bug again and this time I checked right location for logs, i.e. /var/log/...
I didn't see anything interesting, except that /var/log/lightdm/seat0-greeter.log has following error repeatedly: (lightdm-gtk-greeter:3794): Gtk-WARNING **: Drawing a gadget with negative dimensions. Did you forget to allocate a size? (node menubar owner GreeterMenuBar) About my dual display: I forgot to mention that while I have set displays to mirror each other in Xfce settings, this setting does not affect login screen for some reason. -- Markus Laire https://www.MarkusLaire.com